1. Field of the Invention
This invention relates generally to adjustment knobs and is concerned more particularly with a knob assembly having means for controllablyy locking a rotatable shaft in a selected angular position.
2. Discussion of the Prior Art
Control devices, such as valves, timers, rheostats, potentiometers, and the like, generally are provided with a protruding shaft which may be rotated to adjust the device to a desired setting. A coaxially disposed knob may be affixed to a distal end portion of the shaft such that rotation of the knob will produce a corresponding rotation of the shaft. Also, for critically adjusted devices, for example, the knob assembly may include suitable locking means for maintaining the rotatable shaft in a selected angular position until a new adjustment is required.
Thus, U.S. Pat. No. 2,787,353 granted to L. Spraragen discloses a push-to-turn knob assembly having resiliently biased locking means interacting with a plurality of coaxial cylinders for maintaining an axially disposed shaft in a selected angular position. However, locking means of the described type generally involves a plurality of parts having tight dimensional tolerances to avoid undesired interference engagements which may cause malfunction of the knob assembly. Furthermore, these prior art knob assemblies generally are expensive to fabricate and require time consuming operations for assembling the plurality of interacting parts into a relatively complicated structure.
Therefore, it is advantageous and desirable to provide a control knob assembly with comparatively inexpensive and readily assembled means for controllably locking a rotatable shaft in a selected angular position.